Trends in hypertension prevalence, awareness, treatment, and control in South Korea, 1998–2021: a nationally representative serial study

The impact of the pandemic on hypertension management is unknown, particularly regarding changes in demographic risk factors. We conducted a comprehensive study between 1998 and 2021 on the long-term trends in hypertension prevalence in South Korea, including a comparison of the pre-pandemic and pandemic eras. Data from 1998 to 2021 of 108,687 Korean adults were obtained through a nationwide, large-scale, and serial study. We conducted a weighted complex sampling analysis on the estimates of national prevalence and compared the slope of hypertension prevalence before and during the pandemic to determine the trend dynamics. We included 108,687 participants over 24 years, 1998–2021. While the prevalence of patients with hypertension consistently increased before the pandemic from 25.51% [95% CI: 24.27–26.75] in 1998–2005 to 27.81% [95% CI: 26.97–28.66] in 2016–2019, the increasing slope in hypertension prevalence slowed during the pandemic period (28.07% [95% CI: 26.16–29.98] for 2021; βdiff, −0.012 [−0.023 to 0.000]). Hypertension awareness, treatment, control, and control rates among patients receiving treatment followed similar trends. Compared to the pre-pandemic era, individuals aged 19–59 years or male had significantly increased control rates among the treated patients during the pandemic. This study investigated long-term trends in hypertension prevalence, awareness, treatment, and control among Korean adults. The absence of a reduction in the health indicators associated with hypertension during the pandemic implies that medical services for individuals with hypertension remain unaffected.

burden on healthcare resources 2 .Thus, a thorough understanding of trends in hypertension prevalence, awareness, treatment, and control is crucial for developing effective prevention and control strategies 3 .
Furthermore, the COVID-19 pandemic has caused unprecedented disruptions to healthcare systems worldwide [4][5][6] .Consequently, the impact of the pandemic on hypertension management remains unclear, particularly regarding changes in demographic risk factors 7 .By comparing hypertension trends before and during the pandemic, it may be possible to ascertain the effect of the pandemic on hypertension management.
Thus, we aimed to present a comprehensive overview of hypertension trends in South Korea between 1998 and 2021, including a pre-pandemic and pandemic era comparison 8,9 .Additionally, we investigated the socioeconomic factors for hypertension in South Korea and these risk factors variations over time.Our findings will help policymakers and healthcare providers develop a focused treatment plan for hypertension management.

Method Study population
The Korea Disease Control and Prevention Agency (KDCA) conducted the Korea National Health and Nutrition Examination Survey (KNHANES), a nationwide health information survey, using a stratified multistage probability sampling design to obtain nationally representative estimates of the Korean population 10,11 .Sample weights were accounted for by using primary sample units, households, and persons to ensure accurate representation.Each year, health interviews and physical examinations were conducted on a representative sample of the entire Korean civilian population 10,11 .Herein we utilized the KNHANES data from 1998 to 2021 to examine the trends in hypertension prevalence, awareness, treatment, control, and control among patients receiving treatment over 24 years.The study protocol was approved by the Institutional Review Board of Kyung Hee University (KHUH 2022-06-042) and the KDCA.All participants provided written informed consent.The research was carried out in accordance with the principles outlined in the Declaration of Helsinki.
We used 108,824 adults who completed hypertension evaluation; however, 137 were excluded owing to missing weight values.Thus, the final sample for data analysis included 108,687 participants at baseline, 47,062 (43.3%) men and 61,625 (56.7%) women.

Time trend
We aimed to categorize the survey periods based on the investigation phases of KNHANES 10 .To stabilize prevalence, we grouped the first to third phases (1998, 2001, and 2005).Additionally, for the year 2019 corresponding to the 8th phase, we integrated it with the 7th phase and separately analyzed the pandemic period.Finally, to analyze changes during the pandemic period more sensitively, we opted to dissect and analyze the years 2020 and 2021.These years segments were: 1998-2005, 2007-2009, 2010-2012, 2013-2015, 2016-2019, 2020, and  2021.Because the first COVID-19 cases in South Korea were reported on January 20, 2020, we classified 2020 as the early pandemic era and 2021 as the mid-pandemic era 5,12,13 .

Main outcome
The independent variables of this study were hypertension prevalence, awareness, treatment, control, and control among patients receiving treatment 3 .Participants were asked to self-report whether they had been previously diagnosed with hypertension.Subjects rested for over 5 min by sitting, and then the researcher allowed the subjects to properly place the cuff on their arm circumference.Blood pressure was measured using a Baumanometer Wall Unit 33 (mercury sphygmomanometer) from 1998 to 2019, Greenlight 300 (mercury-free auscultatory device) in 2020, and Microlife WatchBP Office AFIB (mercury-free automated blood pressure device) in 2021 14 .The researcher checked the participant's blood pressure two to three times on their right arm.We used the second value or the average of the second and third value of blood pressure for the study.Hypertension was classified as a systolic blood pressure of ≥ 140 mm Hg or a diastolic blood pressure of ≥ 90 mm Hg or being on medication for hypertension 3 .Awareness was determined by the percentage of participants with hypertension who answered "Yes" to the question, "Have you ever been told by a doctor or other healthcare professional that you had high blood pressure?" 3 .Although the guideline of the KNHANES analysis suggested that treatment is defined as the percentage of participants with hypertension who reported receiving more than 20 days of prescribed antihypertensive medication for its management, there was no detailed question about frequency between 1998 and 2005.To ensure consistent analysis, we have defined treatment as follows.Treatment was calculated as the percentage of participants with hypertension who reported receiving at least one prescribed antihypertensive drug for the management of hypertension 3 .Control was calculated as the percentage of participants with hypertension who had a systolic blood pressure < 140 mm Hg and a diastolic blood pressure < 90 mm Hg during the survey measurements.Control among those receiving treatment refers to individuals who are taking medication for hypertension and have a systolic blood pressure < 140 mm Hg and a diastolic blood pressure < 90 mm Hg as determined through measurements obtained during the survey.

Statistical analysis
We conducted a weighted complex sampling analysis to examine the estimates of national hypertension prevalence, awareness, treatment, and control among those receiving treatment.We used the weights to calculate the crude rate.In addition, the age-standardized prevalence rates for hypertension were estimated.We utilized weighted linear regression models to examine the trend of hypertension prevalence, awareness, treatment, control, and control among patients receiving treatment over the last 24 years, focusing on the period during the COVID-19 outbreak 16 .A difference of β (β diff ) and 95% confidence interval (CI) was analyzed to examine the trend changes between 1998 and 2019 vs. 2020-2021 (before vs. during the pandemic) 5,12,17,18 .Additionally, we utilized weighted logistic regression models to obtain the weighted odds ratios (ORs) and 95% CI between 1998 to 2019 versus 2020 to 2021.We performed a stratification analysis by sex, educational background, region of residence, and income through all weighted linear and logistic regression models to confirm our main findings.We calculated the ratio of ORs to estimate the interaction term of each risk factor, which allowed us to identify which groups were more vulnerable to the prevalence of diagnosed hypertension and more likely to have awareness, treatment, control, and control among patients receiving treatment during the pandemic.To robust the hypothesis, we analyzed β diff and ORs by a single year between 2016 to 2019 versus 2020 to 2020.
All statistical analyses were performed using the SAS software (version 9.4; SAS Institute, Cary, NC, USA).We used a two-sided test and considered p-values < 0.05 statistically significant.

Results
Over 24 years, between 1998 and 2021, a comprehensive examination of the KNHANES included 108,687 participants.Table 1 shows the demographic and baseline characteristics of the participants.Of the total participants (mean age 49.97 [standard deviation, 16.78] years), 47,062 (43.3%) were men, whereas 61,625 (56.7%) were women.
Table 2 shows the weighted crude prevalence, awareness, treatment, control, and control among patients receiving treatment stratified by factor groups over 24 years and the trends before and during the COVID-19 pandemic.

Prevalence of hypertension
The study found that there was a statistically significant increase in the weighted prevalence of hypertension from 25.51% (95% CI: 24.27-26.75)to 28.07%(95% CI: 26.16-29.98)between 1998 and 2021 (Table 2 and Table S1-S14).However, the prevalence of hypertension did not increase significantly from the new onset of the pandemic to 2021.Regarding sex differences, the prevalence of hypertension significantly increased in men during the pandemic compared to the pre-pandemic era of 2016-2019 (Table S15 and S16).However, no significant differences were observed in the age group, residence, educational background, or income categories.Table 3 shows the odds ratios (95% CI) and coefficients of hypertension prevalence, awareness, treatment, control, and control among patients receiving treatment during the pre-and pandemic eras.Before the pandemic, the prevalence of hypertension consistently increased between 1998 and 2019.However, the increase in the prevalence of hypertension showed a decrease during the pandemic period compared to the pre-pandemic era (β diff , −0.012; 95% CI: −0.023 to 0.000, p-value < 0.05).This trend was observed in urban areas and across different levels of education (Fig. 1).

Hypertension awareness, treatment, control, and control among patients receiving treatment
The weighted crude rate of awareness steadily increased from 43.41% (95% CI: 41.17-45.65) to 68.08% (95% CI: 66.66-69.50)before the pandemic (1998-2019) and further improved to 74.08% (95% CI: 71.34 When comparing the pre-pandemic era (2016-2019) to the pandemic era, no significant odds ratios were observed for prevalence, awareness, treatment, control, and control among patients receiving treatment, except for men, who showed a significant odds ratio for the prevalence of hypertension (Table S6).However, during the pandemic era, there were significant increases in hypertension awareness, treatment, control, and control among patients receiving treatment.Regarding health indices, the odds ratios for awareness, treatment, control, and control among patients receiving treatment differed significantly between the first and late pandemic eras.Nevertheless, no significant odds ratios were observed for the prevalence of hypertension during the pandemic era compared with the pre-pandemic era or between the first and late pandemic eras.

Socioeconomic factors
Table 4 shows the odds ratios between the pre-COVID-19 and COVID-19 pandemics to identify any changes in risk factors during the pandemic era.The risk factors for hypertension were sex (male), older age (> 60 years), Table 1.General characteristics a of Korean adults, 1998-2021 (total N = 108,687).a Numbers and unweighted proportions (%).b Central obesity was defined as having waist circumference ≥ 90 cm for men and ≥ 85 cm for women.

Key findings
To the best of our knowledge, this is the first study to investigate the long-term trends and the potential impact of the COVID-19 pandemic on hypertension prevalence, awareness, treatment, and control, and its associated socioeconomic factors in South Korea (n = 108,687).We found that the hypertension prevalence increased throughout the pre-pandemic era; however, the increase in hypertension prevalence slowed during the pandemic era.The trends in hypertension awareness, treatment, control, and control among patients receiving treatment were similar.Young adults or men (19-59 years) were recognized as being more likely to benefit clinically after the pandemic era.Suggestions regarding the political implications of a clinical plan that considers hypertension

Comparison with previous studies
Initially, investigations regarding the prevalence, awareness, treatment, control, and control among patients receiving treatment and its associated socioeconomic factors were not conducted in the specific context of the   www.nature.com/scientificreports/COVID-19 pandemic.Our research spans 24 years and aims to provide long-term insights.Prior studies have thoroughly investigated the relationship between hypertension and mortality rates during the COVID-19 pandemic or only the prevalence of hypertension.However, our focus had been on analyzing the patterns of health indicators associated with hypertension prevalence, awareness, treatment, control, and control among patients receiving treatment [19][20][21][22] .Our findings were consistent with previous research on the prevalence, awareness, treatment, control, and control among patients receiving treatment 8,23 .

Ratio of OR (95% CI) p-value Weighted OR (95% CI) p-value Weighted OR (95% CI) p-value Weighted OR (95% CI) p-value
Previous studies have identified various sociodemographic factors for hypertension, but none have examined these factors in the context of the COVID-19 pandemic 24,25 .A previous study reported that individuals > 60 years, men, and those with lower education and income levels were at a greater risk of hypertension 3,26 .However, it is imperative to note that these risk factors remained consistent during the pandemic era.Nevertheless, there may have been some differences in health indices associated with hypertension during this period.

Possible mechanisms
Men and young adults may have had better hypertension control and treatment rates during this period for several reasons.First, the pandemic has led to an increased focus on public health and preventive measures, including managing chronic conditions such as hypertension 27 .The pandemic has heightened awareness of the significance of health.Individuals with chronic ailments, like hypertension, may be more inclined to manage their overall well-being diligently.As a result, there may be increased awareness among men and young adults regarding the importance of hypertension control and treatment, leading to better adherence to medication and lifestyle modifications.Second, telemedicine and remote monitoring have become more common during the pandemic 28 , making it easier for men and young adults to receive hypertension treatment and monitoring from the safety of their homes 29 .During the pandemic, healthcare organizations increased their use of in-person care, facilitating hypertension patients' access to healthcare and potentially improving blood pressure management.This may have led to increased access to healthcare and improved hypertension control and management 30 .Furthermore, the pandemic and lifestyle changes, such as reduced stress levels due to remote work or reduced commuting time, can positively impact hypertension control and treatment outcomes 31 .During the pandemic, individuals have been spending more time in their homes, potentially creating an environment that promotes a focus on health.The decrease in outdoor activities and increase in home-based routines may have contributed to this heightened awareness.For instance, implementing healthy meal choices or engaging in routine exercise may positively affect blood pressure management.Additionally, During the pandemic, there has been a significant www.nature.com/scientificreports/improvement in the accessibility of health information through online platforms 32 .This has allowed patients to easily access vital information and gain a better understanding of their condition, which may have enabled them to adopt necessary lifestyle changes to manage their blood pressure effectively.

Policy implications
Based on our study, the Korean clinical system effectively maintained health indices related to hypertension during the pandemic 33 .Further research should be conducted to better understand this clinical system.Additionally, this clinical system should be considered for treating morbidities other than hypertension.Behaviors of young adults and men aged 19-59 years should be analyzed to develop interventions that can be applied to all patients with hypertension as they showed higher performance regarding health indices related to hypertension.This can lead to significant improvements in the treatment and management of hypertension, although its incidence cannot be prevented.Based on our understanding of the existing clinical system, we must not ignore any potential weaknesses in the clinical infrastructure in preparation for future pandemic eras.
During the COVID-19 pandemic, we observed a deceleration in the rate of hypertension prevalence increase.This finding implies that preventative healthcare strategies and hypertension management policies can be successfully sustained even amidst a pandemic.Therefore, other nations can mitigate the negative impact of the COVID-19 crisis by implementing and promoting policies and initiatives aimed at enhancing hypertension prevention and management.

Strengths and limitations
Our study has several strengths, including a large sample size, representative data from the Korean population, a comprehensive investigation of 24-year trends and risk factors in hypertension prevalence, awareness, treatment, and control, and a comparison between the pre-and COVID-19 pandemic eras.However, our study has some limitations.First, regardless of the length of treatment, the definition of hypertension treatment has changed over time, encompassing patients receiving antihypertensive medication.This inconsistency in the description of treatment across different periods in the KNHANES might have led to an overestimation of the rate of hypertension treatment from 1998 to 2005.Despite the potential limitations of our study, the overall impact on the trend is anticipated to be minimal, given the consistency of the definitions used in the latter periods and the absence of significant gaps in the existing literature.Furthermore, although our investigation centers on a pandemic with a relatively brief duration, it can serve as a viable surrogate for future research.Our research examined socioeconomic demographic changes over 24 years, including significant urbanization 34 .Thus, while our findings may not provide a definitive understanding of the trend, they have great academic value due to the duration of our study.To accurately reflect the actual trend, we treated non-responses to the questionnaire or "unknown" responses as negative responses, which had a negligible impact on the results and did not create any noticeable limitations.

Conclusions
This study investigated long-term trends in the prevalence of hypertension and its related awareness, treatment, and control among Korean adults.We found that the prevalence of hypertension increased before the pandemic but slowed during the pandemic.The prevalence of hypertension was the highest in 2021, with rates of awareness, treatment, and control following a similar trend.This study suggests that young adults and men should receive clinical benefits after the pandemic.The absence of a reduction in the health indicators associated with hypertension during the pandemic implies that medical services for individuals with hypertension remain unaffected.Furthermore, the increase in health indices indicated that the Korean clinical system was effectively activated during the pandemic.

Figure 1 .
Figure 1.Nationwide trends in hypertension prevalence, awareness, treatment, and control among Korean adults, 1998-2021.Markers represent the mean ratio.The horizontal lines indicate 95% confidence interval.

Table 2 .
National trend of the weighted crude prevalence, awareness, treatment, control, control among treated before and during the COVID-19 pandemic, 1998-2021.CI confidence interval.

Table 3 .
Weighed trend of hypertension prevalence, awareness, treatment, control, and control among treated: estimated β-coefficients and weighted odds ratios with 95% CIs.CI confidence interval.Numbers in bold indicate a significant difference (P < 0.05).

Table 4 .
Ratio of ORs for association between the prevalence, awareness, treatment, control, and control among treated of hypertension and each socioeconomic factor, 1998-2021.CI confidence interval.Numbers in bold indicate a significant difference (P < 0.05).